3D Printing

It's one of those thingies with
all the little bits attached.  
Bob

No sane person could even fathom what goes on inside your mind, so how are we supposed to guess at what comes out of it?  

Well really! Implications that I'm bonkers!

Here it is ready to use.



He'd fly through the air with the greatest of ease, That daring old man on the flying trapeze.

I was only kidding of course....we love ya Ian!

Hmm, model airplane storage? Some kind of hangar hanger perhaps?

Spray paint lazy susan?

So it is a sort of center of gravity measuring device?

Phil

pkrankow wrote:So it is a sort of center of gravity measuring device?

Phil

A very accurate centre of gravity measuring device?

ian1954 wrote:

pkrankow wrote:So it is a sort of center of gravity measuring device?

Phil

A very accurate centre of gravity measuring device?

It seems you type with a British accent. (center vs centre)

Yes, on reviewing the video I see the function of it.

Phil

However, don't let the previous video fool you into thinking that the plane was nose heavy.

It was tail heavy - how do I know? I had a disastrous flight with it after following the instructions on the kit for the CoG position! It said 100mm (4") behind the leading edge. I thought it strange and soon found how uncontrollable a tail heavy aeroplane is! Followed by the walk of shame!




You set the trapeze so that the model is at its flying level position or (tech. speak) its datum line is horizontal.



Once level, the plumb line will indicate the centre of gravity. These pictures are after adding 15g of weight to the front.

So...why does it need to rotate freely?

Phil

Interesting question? Hope I can explain.

The strings are looped around the bobbins to prevent them slipping but the bearings allow the plane to settle. The strings are then adjusted on the plane to bring it flight level. As you move the strings the bobbins turn freely but the string doesn't slip.

As you adjust the strings and the plane stays level (it is still free to rotate) the plumb bob indicates the C of G.

Add weight to the nose and the plane will tip forward.

Adjust the position of the strings on the plane again to bring it level and the plumb bob will indicate the new C of G further forward.

The strings must not slip freely or the plane will nose down or tail up!

Simply sliding the strings forwards or backwards on the plane brings it level and the freely rotating bobbins automatically adjust the strings so that the bobbins are directly over the C of G.

The freely rotating bearings allow the minutest adjustment, the bobbins (and the loop around them) prevent the strings slipping.

The C of G is not indicated until the plane is level.

So how big of a TD do you want to make?

Well, I'll be darned.

That looks very good Jason! What color is it? It appears to be grey in the picture.

Ron

It is white. Bad camera lighting. I need to modify the part to make the venturi support a bit thicker. It likes to collapse during the print even with support. This was scaled up 2x from the original file which I got off of grabcad.

That is a nice looking print - I am having trouble with small prints collapsing or looking too "stringy" but the larger ones are coming along a treat.

When I get a little more time I will post a few more pictures.

I joined Gabcad the other day but find "searching" on there a little difficult.

Ian, I keep starting to ask questions about your C/G locator, but hesitate and think more about it. Suspension string location, mostly. Very interesting.

Rusty

RknRusty wrote:Ian, I keep starting to ask questions about your C/G locator, but hesitate and think more about it. Suspension string location, mostly. Very interesting.

Rusty

The way it works is simple but more complicated than it looks. I have a few more planes to balance and I will video it (when I get the time - busy finishing things off so that I can tidy up for Christamas!) because it is very accurate. I find it better than the Great Planes thingy I have as it works with very light models. The Great Planes thingy needs planes of a certain weight.

I found a stack of new skate bearings while cleaning out my son's room prior to our yard sale. I kept them, and now will use a couple to make one of these balancers. Thanks for the idea.

Rusty

Remember -

You move the strings along the fuselage until the plane is level and then the plumb bob indicates where the C of G is.

Add weight to correct - re level the plane - and then check where the plumb bob is pointing.

Repeat until the C of G is where you want it to be.

Could one just suspend the model by a single string at the CG point and add or remove weight to make the plane level?

Cribbs74 wrote:Could one just suspend the model by a single string at the CG point and add or remove weight to make the plane level?

Yes. Using fingers, pencils, or other under the wing support is another option too.

This is just a different way to skin the cat, so to speak.

I suspect this would function without the bearings, or any other added fanciness.

Phil

Cribbs74 wrote:Could one just suspend the model by a single string at the CG point and add or remove weight to make the plane level?

Yes you could but how would you attach the string. A solid upper wing or a profile fuselage - easy, a hook secrewed in at the C of G point. but ....... if the screw comes out!

On a built up plane - things get more difficult - for example, if the canopy is on the C of G.

I balanced the NightHawk by supergluing a bent pin in the upper wing - left it there. Then realised that i needed to change the C of G.

I suppose all methods are good but have limitations.